1. Field of the Invention
The present invention is related to an easy removed die core device used for cold swaging, and especially to an easy removed die core device, wherein, by means of a plurality of screw typed outer and inner tension springs and by the nature that the diameter of any ring on the threads of the springs can be elastically reduced when it is compressed, the swaging force exerted on the wall of the blank to be forged can be resisted by the elastic die core device, and after swaging, the elastic die core device can be taken out of the inner wall of the shaped workpiece easily, and the rough edges on the inner wall formed in swaging can be planed by the angled edges of a plurality of rings of the threads on the outer spring.
2. Description of the Prior Art
In processing metallic workpieces, forging techniques have been well used to increase the strength of the workpieces, normally, workpieces which are abrasion resistant, compression resistant, shearing resistant etc . . . are used for forging. The ways of forging available in the field include the rotary swager, the stationary-spindle swager, the creeping-spindle swager, the alternate-blow swager and the disclosing swager, etc . . . ; such existing swaging techniques can be used for processing a solid forged workpiece 1 (as shown in FIG. 1) and a hollow pipe forged workpiece 10 (as shown in FIG. 2); however, a hollow pipe forged workpiece must be examined for the easiness for extending therethrough a die core before swaging, and for the feasibility that the die core can be taken out of the inner wall of the hole of the shaped workpiece, these two points generally prevent some hollow workpieces with special shapes from swaging for enhancing their strength.
Therefore, we now take the hub used on a wheel of a bicycle as an exemplifying workpiece for explanation:
As shown in FIG. 1, there is depicted the above mentioned conventional technique in cold forging the solid workpiece 1, wherein, a gradually proceeding forging step must be used in order to gradually forge and shape the solid workpiece 1 to form an arciform exterior wall 11, two end annular portions 12 of a hub of the wheel 13, then the annular portions 12 are drilled to form the necessary hooking holes 14, the hub of the wheel 13 is further processed with a milling knife 15 to form a bore with an inner wall 161, and the solid workpiece 1 thereby is formed a shaped wheel hub 16; however, this forging and milling method is overly material and cost consumptive, and it has been added with a boring process, in this view, the outstandingly high cost of material as well as processing has left to it a big problem; moreover, in the pipe walls of a completed wheel hub 16 (referring to FIG. 3), grainfiber flow 17 thereof has been observed with a metallographic microscope and has found that the wheel hub 16 made through the process of boring had damaged partial of the grainfiber flow 17, this has rendered the crystallines after swaging to have had uneven distribution of stress, therefore, the strength of the completed wheel hub 16 can not give the desired requirement of compression strength, this is one of the disadvantages of such a conventional technique.
Secondly, As shown in FIG. 2, there is depicted the above mentioned conventional technique in cold forging the hollow pipe workpiece 10 for forming a completed wheel hub 16, wherein, the rotary swager as mentioned above is used in the forging process, it is impossible to place a die core into the bore 101 of the wheel hub 16 having an arciform inner wall 104 (classified as one of the abovementioned special shapes) by the forging process, hence only smaller forging pressure can be used by way of progressive rotary swaging on the hollow pipe workpiece 10 to gradually swage and shape an arciform exterior wall 102, the arciform inner wall 104 and two end annular portions 103 to form a shaped wheel hub 106, then the annular portions 103 are drilled to form the necessary hooking holes 105,the shaped workpiece is thereby completed by such a conventional method; however, this forging method on the hollow pipe workpiece 10 is proceeded without a die core, so that the capability of the hollow pipe workpiece 10 for resisting rotary swaging force is smaller although the hollow pipe workpiece 10 does not require a milling process for boring which can increase the cost of material and processing, in this view, only the hollow pipe workpiece 10 with thinner wall can be forged by this method, and those hollow pipe workpieces require higher compressive strength can not, this makes an undesired limitation of such a method; moreover, a shaped wheel hub 106 form with the hollow pipe workpiece 10 has been found with a metallographic microscope that, on the wall portion thereof where a larger forging action is applied on (such as is shown in FIG. 4), the grainfiber flow 107 therein shows weakness by a crowed phenomenon in which acute angles are in the grainfiber flow 107 by virtue that the inner wall 104 does not have a resistive die core, the crystallines thereof where the swaging force is more concentrated are very weak, such area of the shaped wheel hub 106 is most fragile and subjected to breakage, this is the most troublesome problem of such a method.